Parentage analysis of multi-male social groups of tasmanian native hens (Tribonyx mortierii): genetic evidence for monogamy and polyandry

Accurate estimates of male reproductive success are essential to understanding the evolution of polyandrous mating systems. Here, we use multilocus DNA fingerpinting to assess parentage in an island population of Tasmanian native hens (Tribonyx mortierii), which often live in multi-male and/or multi-female social groups. This isolated population presented special challenges to this technique because it was artificially founded from a small number of individuals in the recent past. DNA profiles from four multilocus minisatellite probes were analyzed for adults and offspring from six social groups using two methods: (1) significance of band-sharing coefficients and (2) distribution among a group's offspring of fragments unique to certain adults. Traditional band-sharing analyses did not provide sufficient resolution to establish parentage in this population due to the high level of band-sharing between adults within groups. In contrast, the distribution of unique fragments suggests that in most cases, all offspring within a group have the same male and female genetic parents, so that monogamy may be the predominant genetic mating system of this species. This forces a rexamination of the evolutionary basis of polyandry in these birds. It also demonstrates some of the difficulties in using these highly polymorphic genetic markers for parentage analyses when putative parents are closely related.     

Brood parasitism and cooperative nesting in the moorhen,Gallinula chloropus

Summary During a two year study of the moorhen, Gallinula chloropus, a quarter of the nests found had two or more females laying in them. This was the result of two features of the moorhens' breeding biology: (1) Cooperative nesting; two (or more) females were paired to the same male. Both laid in the same nest, the second laid a large clutch synchronously to the first, and both cooperated in parental care. (2) Intraspecific brood parasitism; some females (parasites or dumpers) laid a small number of eggs at random in the nests' of neighbours. Cooperatively nesting females were mother and daughter, while parasite and host were not. Parasitic females laid in their own nest as well, and generally did so after completing a dumping sequence. Parasitic eggs were laid at random during the host's laying and incubation period, and were about a quarter as likely to produce an independent chick as were non-parasitic eggs. Parasitic females would probably have reared more chicks by laying in their own nests straight away, instead of dumping any eggs at all, because there was a strong decline in reproductive success with season. Possible reasons why they did not do so are discussed. Parasitised pairs tended to rear fewer own chicks than non-parasitised pairs. There was no evidence that hosts selectively destroyed parasitic eggs. Four hypotheses that explain why hosts accepted dumped eggs are considered. (1) The host pair were unaware of the dump, (2) the host male had copulated with the dumping female, (3) the dumper was related to one of the host pair, and (4) there was a benefit to the host pair because they gained extra helpers. These hypotheses were not supported by the data, but further tests are needed. As the cost of desertion was greater than the cost of acceptance of parasitic eggs, hosts may have been forced to accept.     

Larval development in the Tasmanian mysids Anisomysis mixta australis, Tenagomysis tasmaniae and Paramesopodopsis rufa (Crustacea: Mysidacea)

We describe the brood duration and marsupial development of three temperate coastal mysid species, Anisomysis mixta australis (Zimmer), Tenagomysis tasmaniae Fenton and Paramesopodopsis rufa Fenton, found commonly in Tasmanian waters. Larvae cultured in vitro had brood durations at 13 °C (17 °C) of 22 (15), 23 (15), and 28 (20) d, respectively. Development through seven larval stages, and brood durations for these three species are similar to those reported for coastal mysids from other temperate areas throughout the world. Received: 10 June 1997 / Accepted: 1 July 1997     

Ecological gradients and relative abundance of native (Mytilus trossulus) and invasive (Mytilus galloprovincialis) blue mussels in the California hybrid zone

Marine communities are experiencing unprecedented rates of species homogenization due to the increasing success of invasive species, but little is known about the mechanisms that allow a species to invade and persist in a new habitat. In central California, native (Mytilus trossulus Gould 1850) and invasive (Mytilus galloprovincialis Lamarck 1819) blue mussels and their hybrids co-exist, providing an opportunity to analyze the mechanisms that determine the distributions of these taxa. Spatial and temporal variation in temperature and salinity and the relative frequencies of these mussel taxa were examined between 2000 and 2004 at four sites in San Francisco Bay and four in Monterey Bay, which were chosen for their different positions along inferred estuarine/oceanic gradients in the hybrid zone. Mussels were genetically identified as the parent species or hybrids by amplifying regions of two species-specific loci: the adhesive byssal thread protein (Glu-5′) and the internal transcribed spacer region of ribosomal DNA (ITS 1). The proportion of M. trossulus at the eight hybrid zone sites correlated negatively with average salinity (R ²=0.60) and positively with maximal temperature (R ²≥0.72), a somewhat unexpected result given what is known about the phylogeography of this species. The proportion of M. galloprovincialis showed the opposite pattern. The proportion of hybrids was correlated neither with habitat temperature nor salinity. Genotypes of mussel populations at an additional 13 sites from Coos Bay, Oregon (latitude 43.35°N) to Long Beach, California (latitude 33.72°N), sampled at various intervals between 2000 and 2004, were also determined. This survey confirmed previous reports that the hybrid zone lies between Monterey and the Cape Mendocino region (latitudes 36.63°N–40.5°N). Within Monterey and San Francisco Bays, however, the temporal comparisons (1990s vs. 2000s) revealed abrupt changes in the proportions of the two parent species and their hybrids on annual and decadal time scales. These changes indicate that the blue mussel populations are in a highly dynamic state. The survey also showed that, regardless of habitat, M. trossulus is consistently of smaller average size than either M. galloprovincialis or hybrids.

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Trophic ecology of New Zealand triplefin fishes (Family Tripterygiidae)

In many vertebrate radiations, food partitioning among closely related taxa is a key factor in both the maintenance of species diversity and the process of diversification. We compared diet composition and jaw morphology of 18 New Zealand triplefin species (F. Tripterygiidae) to examine whether species have diversified along a trophic axis. These fishes predominantly utilised small, mobile benthic invertebrates, and interspecific differences in diet composition appeared to be mainly attributable to habitat- or size-dependent feeding behaviour. Although there were differences in the relative size of the bones comprising the oral jaw apparatus between species, the majority showed an apparatus consistent with a relatively high velocity, low force jaw movement indicative of a diet of evasive prey. Phylogenetic comparative analyses showed that the evolution of jaw lever ratios and diet breadth was best explained by a non-directional model in which character changes have occurred randomly and independent of phylogeny. The mode of diet breadth evolution was gradual and the tempo has not accelerated or slowed down over time. The mode of evolution for the jaw lever ratios has been gradual for the opening but punctuated for the closing levers, suggesting that evolutionary changes have occurred rapidly for the latter trait. The tempo of trait evolution for the jaw opening levers has not accelerated or slowed down over time, while the tempo for the jaw closing levers has accelerated towards the tips of the tree, which is suggestive of species level adaptation. The lack of phylogenetic signal in diet breadth and jaw lever ratios appears most likely to be a correlated response to the marked habitat diversification in this group, and is thus the passive outcome of prey availability in species-specific habitat types. Overall, the trophic ecology of New Zealand’s triplefin fauna parallels the generalist strategy typical of the family worldwide, suggesting that trophic resource partitioning has not been an important factor in the evolution of these fishes. Electronic supplementary material  The online version of this article (doi:) contains supplementary material, which is available to authorized users.     

Marine Gammaridea (Crustacea: Amphipoda) from the Indian region. Family Ampithoidae

This paper deals with 6 species of marine gammaridean amphipods belonging to the family Ampithoidae. The specimens described were collected from Mandapam (Gulf of Mannar), India and Thankasserry (Quilon, Kerala), India. The collection includes 3 new species, namely Ampithoe (Ampithoe) serraticauda, Ampithoe (Pleonexes) auriculata and Cymadusa imbroglio. Ampithoe (Ampithoe) kergueleni Stebbing (1888) is a new record for this region, while Ampithoe (Ampithoe) ramondi Audouin (1826) and Cymadusa filosa Savigny (1816), the two well-known tropicopolitan members, are briefly redescribed. The study supports Barnard's (1970, p. 23) contention that the genus Pleonexes Bate (1857) (since reduced to subgeneric status under the genus Ampithoe Leach, 1814) represents only a grade of evolution, but suggests that the structure of the 1st maxillary and mandibular palps and the outer lobes of the lower lip should also be taken into consideration, in combination with the telsonic processes, for distinguishing Pleonexes from Ampithoe. Based on this concept, a reappraisal of some of the species of the genera is suggested. The subgenus Ampithoe is created to hold those species of Ampithoe showing typical characteristics of the genus.     

Antipredator responses of koomal (Trichosurus vulpecula hypoleucus) against introduced and native predators

Antipredator behavior studies generally assess prey responses to single predator species although most real systems contain multiple species. In multi-predator environments prey ideally use antipredator responses that are effective against all predator species, although responses may only be effective against one predator and counterproductive for another. Multi-predator systems may also include introduced predators that the prey did not co-evolve with, so the prey may either fail to recognize their threat (level 1 naiveté), use ineffective responses (level 2 naiveté) or succumb to their superior hunting ability (level 3 naiveté). We analyzed microhabitat selection of an Australian marsupial (koomal, Trichosurus vulpecula hypoleucus) when faced with spatiotemporal differences in the activity/density levels of one native (chuditch, Dasyurus geoffroii) and two introduced predators (red fox, Vulpes vulpes; feral cat, Felis catus). From this, we inferred whether koomal recognized introduced predators as a threat, and whether they minimized predation risk by either staying close to trees and/or using open or dense microhabitats. Koomal remained close to escape trees regardless of the predator species present, or activity/density levels, suggesting koomal employ this behavior as a first line of defense. Koomal shifted to dense cover only under high risk scenarios (i.e., with multiple predator species present at high densities). When predation risk was low, koomal used open microhabitats, which likely provided benefits not associated with predator avoidance. Koomal did not exhibit level 1 naiveté, although further studies are required to determine if they exhibit higher levels of naiveté (2–3) against foxes and cats.     

Population genetics of the northern Pacific seastar Asterias amurensis (Echinodermata: Asteriidae): allozyme differentiation among Japanese,Russian, and recently introduced Tasmanian populations

The northern Pacific seastar Asterias amurensis Lütken was recently introduced to Tasmanian waters, possibly through ballast water discharged from ocean-going vessels. Three Tasmanian populations and seven native populations from Japan and eastern Russia were examined in 1994 for variation at 22 allozyme loci. There was significant spatial heterogeneity in gene frequencies among the native populations, especially for the ocus APK ^*, where G _ST was a very high 0.47. The Tasmanian populations could not be separated genetically from one another, suggesting they have a common origin from a single introduction. The average heterozygosity per locus of the Tasmanian populations (0.116 to 0.127, mean 0.123) was 30 to 40% less than that of the native populations (0.177 to 0.216, mean 0.192), suggesting that colonisation of Tasmanian waters was accompanied by a population-size bottle-neck. The Tasmanian seastars were genetically more closely related to the two populations from central Japan (Suruga and Tokyo Bays) than to populations from Vladivostok, northern Japan (Yoichi, Nemuro and Mutsu Bays) or southern Japan (Ariake Sea). However, there were significant differences between the populations from Tasmania and central Japan, which may be attributable to founder effects or may mean that the true source of the Tasmanian introduction has yet to be identified.     

Compensating for the costs of polygyny in hen harriers Circus cyaneus

In polygynous species, the adults are faced with a dilemma during chick rearing. Males must decide how to distribute food between their females and food allocation patterns are often highly unequal. In turn, the females that receive less food from males have to decide how much time to invest in additional hunting. If they spend more time hunting, then they leave their young exposed to weather and predators. However, if they stay at the nest, they increase the risk of their chicks starving. One way that birds may compensate for reduced provisioning is by increasing the size of prey caught. We tested this hypothesis by comparing prey deliveries to nests of hen harriers, Circus cyaneus, with females of different breeding status. As expected, male harriers delivered less food items to the nests of polygynous females, and especially their secondary, or β females. However, both sexes were able to compensate by delivering larger items and there was no difference in the overall mass of food delivered to nests. Moreover, females spent a similar amount of time at the nest, irrespective of status, and there were no overall differences in breeding success. Our results show that polygynous female harriers can compensate for the costs of polygyny, but we suggest that their ability to do so will vary according to the abundance of both large prey and predators.     

Family insurance: kin selection and cooperative breeding in a solitary primate (Microcebus murinus)

Lactation imposes substantial physiological costs on mothers and should therefore not be directed towards foreign offspring. Such allonursing, however, is common in mammal species that share roosts. Hypotheses to explain allonursing among such plural breeders include misdirected parental care, milk evacuation, brood parasitism, reciprocity, and kin selection. The necessary behavioral data, in combination with data on kinship and kin recognition, have rarely been available to distinguish among these explanations, however. In this study, we provide evidence for cooperative nursing and adoption by plural-breeding females in a nocturnal primate, the gray mouse lemur (Microcebus murinus), in which females forage solitarily during the night, but form day-time sleeping groups with one to two other females. We observed 34 resident females in an 8 ha study area in Kirindy Forest, Madagascar, over three consecutive annual breeding seasons and determined genetic relationships among all members of this population. Five sleeping groups of adult females were filmed inside their roosts during one breeding season after females gave birth. The composition of groups changed substantially across years, but they always consisted of close maternal relatives. All females within a group gave birth to one to three infants. They regularly transferred only their own offspring among roosting sites, demonstrating an ability to discriminate between their own and other’s offspring, but they regularly groomed and nursed related offspring other than their own and adopted related dependent young after their mother’s death. Kin selection may therefore be the main selective force behind cooperative breeding among these closely related females with a high mortality risk, providing each of them with family insurance.     

乡土植物在广梧高速公路生态绿化中的应用

绿化关系到高速公路的长期效益,是生态高速公路建设的重要内容。广梧高速公路的生态绿化,以利用乡土植物为原则,模拟自然生态系统的组成和结构,实现公路景观与周边自然景观的和谐统一。对广梧高速公路双凤至平台段的自然条件、植被类型及植物种类进行了全面调查,结果显示该地域共有维管束植物342种,隶属于95科244属,然后结合植物本身的生物学、生态学及生理学特征,从中筛选出适于本段高速公路两侧绿化带、边坡绿化的乡土植物53种;并根据沿线具体的生境条件,按照群落学的原则对其组合应用进行了设计。     

The behavioural basis of a species replacement: differential aggresssion and predation between the introduced Gammarus pulex and the native G. duebeni celticus (Amphipoda)

Previous studies have shown that differential predation by males on moulted female congenerics may be largely responsible for the elimination and replacement of the native Irish freshwater amphipod Gammarus duebeni celticus by the introduced G. pulex. Predation of moulted females occurs both shortly after their release from precopulatory mate-guarding and whilst they are being guarded by their mates. In the present study, two hypotheses concerning the underlying cause(s) of the differential predation pattern are tested. Firstly, female G. d. celticus may be more vulnerable to predation than female G. pulex due to the former being released from precopula guarding with the new exoskeleton in a less hardened state. Secondly, G. pulex may be an inherently more aggressive species than G. d. celticus during predatory interactions over guarded females. The first experiment indicated that differential predation was not mediated by species differences in the state of the female exoskeleton at the time of release from precopula by guarding males. The second experiment, however, showed that male G. pulex were significantly more aggressive than male G. d. celticus in attacking both guarding male congenerics and guarded moulted female congenerics. In addition, in defence against predatory attacks, paired male and female G. pulex were significantly more aggressive than paired male and female G. d. celticus. These differences in aggressive behaviour led to a significantly higher frequency of predation on G. d. celticus females than on G. pulex females, and also explains this finding in previous studies. It is concluded that differential predation due to differences in aggressive behaviour may explain the pattern of replacement between these species.     

Phylogeography of two Atlantic squirrelfishes (Family Holocentridae): exploring links between pelagic larval duration and population connectivity

Genetic surveys of reef fishes have revealed high population connectivity within ocean basins, consistent with the assumption that pelagic larvae disperse long distances by oceanic currents. However, several recent studies have demonstrated that larval retention and self-recruitment may be higher than previously expected. To assess connectivity in tropical reef fishes, we contribute range-wide mtDNA surveys of two Atlantic squirrelfishes (family Holocentridae). The blackbar soldierfish, Myripristis jacobus, has a pelagic juvenile phase of about 58 days, compared to about 71 days (~22% longer) in the longjaw squirrelfish, Holocentrus ascensionis. If the pelagic duration is guiding dispersal ability, M. jacobus should have greater population genetic structure than H. ascensionis. In comparisons of mtDNA cytochrome b sequences from 69 M. jacobus (744 bp) and 101 H. ascensionis (769 bp), both species exhibited a large number of closely related haplotypes (h=0.781 and 0.974, π=0.003 and 0.006, respectively), indicating late Pleistocene coalescence of mtDNA lineages. Contrary to the prediction based on pelagic duration, M. jacobus has much less population structure (φ_ST=0.008, P=0.228) than H. ascensionis (φ_ST=0.091, P<0.001). Significant population partitions in H. ascensionis were observed between eastern, central and western Atlantic, and between Brazil and the Caribbean in the western Atlantic. These results, in combination with the findings from 13 codistributed species, indicate that pelagic larval duration is a poor predictor of population genetic structure in Atlantic reef fishes. A key to understanding this disparity may be the evolutionary depth among corresponding taxonomic groups of “reef fishes”, which extends back to the mid-Cretaceous and encompasses enormous diversity in ecology and life history. We should not expect a simple relationship between pelagic larval duration and genetic connectivity, among lineages that diverged 50–100 million years ago.     

Invertebrate introductions in marine habitats: two species of hydromedusae (Cnidaria) native to the Black Sea,Maeotias inexspectata and Blackfordia virginica,invade San Francisco Bay

The hydrozoans Maeotias inexspectata Ostroumoff, 1896 and Blackfordia virginica Mayer, 1910, believed to be native to the Black Sea (i.e. Sarmatic) and resident in a variety of estuarine habitats worldwide, were found as introduced species in the Petaluma River and Napa River, California, in 1992 and 1993. These rivers are mostly-estuarine tributaries that flow into north San Francisco Bay. Both species appeared to be well-established in this brackishwater habitat. Salinities at the collection sites were about 11 during the summer, rising to nearly 20 in the early autumn and falling to near 0 in the winter. Large numbers of all sizes of both species of medusae were observed and collected, indicating that the hydroid stages of the life cycles of the two are also well-established in these rivers. In the Petaluma River, populations of both species were at maximum in late July, with numbers of individuals declining through August and into September; the Napa River was sampled only in October, and at that time only B. virginica was found. Examination of full guts of M. inexspectata and B. virginica medusae revealed that both species had fed nearly exclusively on small crustaceans, principally barnacle nauplii, copepods and their eggs and nauplii, and crab zoea larvae (M. inexspectata only). All the M. inexspectata medusae were males, indicating that the population has probably developed from the introduction of perhaps only a single male polyp or polyp bud. In spite of its inability to reproduce sexually, this population appears to be maintained by the prodigious ability of the polyp to bud and reproduce asexually, and is fully capable of invading additional low-salinity habitats from its present Petaluma River site. Male and female B. virginica medusae were collected in both the Petaluma River and the Napa River, indicating that B. virginica may have been introduced by either the polyp or medusa stage (or both), but that multiple individuals (of both sexes) must have arrived from another port in one or more invasions. As indicated for M. inexspectata, the B. virginica population will also probably seed new populations in San Francisco Bay and elsewhere. Based on its cnidome as well as the morphology of both medusa and polyp, M. inexspectata has been reclassified by moving it from the family Olindiidae, Limnomedusae, to the family Moerisiidae, Anthomedusae.     

Distribution and seasonal abundance of Polygordius spp. (Class: Polychaeta; Family: Polygordiidae) exo- and endolarvae in the southern Mid-Atlantic Bight,USA

The importance life history plays in understanding population dynamics and the functional roles of species for predicting climate change scenarios are well established. Yet, in the marine environment, the complete life history is unknown for many species, especially the link between morphologically and ecologically distinct planktonic larvae, and their corresponding benthic adult forms. Integration of meroplankton abundance, benthic adult species, larval morphology, and molecular data was employed to unravel the complete life history of Polygordius, a dominant polychaete in sandy shelf sediments of the Mid-Atlantic Bight. Polygordius species are unusual, having two distinct planktonic larval forms: an exolarva and an endolarva. Extensive sampling in the southern Mid-Atlantic Bight with careful preservation of meroplankton (2006–2007) revealed the identity of multiple stages of exo- and endolarvae, and their spatial, seasonal, and vertical distribution. Molecular and morphological evidence indicated exolarvae are Polygordius jouinae and endolarva are an undescribed species. Structure and development of these larvae differed greatly. P. jouinae exolarvae were found off Delaware Bay to North Carolina. At some stations, they were abundant, with densities up to 4,013 m^?3, comprising >90 % of the total meroplankton. Exolarvae spent up to a month in the plankton starting in March/May depending on year, settlement began in July when larvae were at least 2 mm in length, and by October were no longer observed in the plankton. These findings are consistent with the distribution patterns and life cycle known for adults. This is the first report of endolarvae north of Cape Hatteras.     

Genetic structure in native and non-native populations of the direct-developing gastropod Crepidula convexa

In many marine invertebrate species, larval development plays an important role in population connectivity and gene flow: species with direct benthic development generally show more genetic structure than those with planktonic development. We used nuclear markers (microsatellites) to determine population genetic structure of the direct-developing snail Crepidula convexa (Gastropoda: Calyptraeidae) in seven populations with 15–85 individuals each within its native range of the northwest Atlantic and compared it to Crepidula fornicata, a congener with planktonic development. Our results are consistent with general expectations and previous work in these species with other markers: C. convexa had greater population structure and even at a regional scale shows significant isolation-by-distance, in contrast to C. fornicata. We also genotyped a single population of C. convexa introduced to the northeastern Pacific to investigate the prediction of reduced genetic diversity following introduction (founder effect). We did not find a reduction in genetic diversity, suggesting that this non-native population may be characterized by multiple introductions. This pattern is consistent with many other introduced populations of marine invertebrates, including C. fornicata.     

Variation in resource availability changes the impact of invasive thistles on native bunchgrasses.

The threat posed by invasive nonnative plants to native plant populations is one of the largest challenges facing both conservation biology and restoration ecology. California has been highly impacted by invaders, although many relict stands of native plants are found on shallow, rocky soils with limited resources. The abiotic conditions of these sites may strongly influence the performance of an invasive plant and its effect on resident native species. In addition, the maturity of native plants in these sites may modulate an invader's impact; larger, well-established plants may be better able to resist invaders. In this study we examined how the impact of an invasive thistle (Centaurea solstitialis) on a native perennial bunchgrass (Nassella pulchra) changed in response to variation in soil depth, soil water availability, and bunchgrass maturity. We measured plant performance in terms of survival, growth, reproduction, and predawn water potential. We found that soil depth, water availability, and bunchgrass maturity acted in concert to influence the impact of the invasive thistle on the native bunchgrass. Both species performed better in deep soils, especially during dry years. The combination of shallow soil and low water availability reduced C. solstitialis performance and ameliorated its negative effect on N. pulchra growth and reproduction. Higher water availability resulted in a stronger negative effect of C. solstitialis on N. pulchra in both shallow and deep soils. However, as N. pulchra matured and increased in size, we saw a steady decline in C. solstitialis growth and reproductive output. Higher water availability increased the performance of C. solstitialis in shallow soils. C. solstitialis may thus have a stronger impact on N. pulchra and be more able to invade relict stands of N. pulchra in shallow soils during high-rainfall years. However, established stands of N. pulchra appear to be more resistant to invasion by C. solstitialis as N. pulchra plants grow older and larger.     

Herbicide exposure affects the chemical recognition of a non native predator in common toad tadpoles (<Emphasis Type="Italic">Bufo bufo</Emphasis>)

Summary. In amphibians and fishes, evidence is increasing that chemical cues from injured conspecifics can play a role in the chemical labelling and learned recognition of unfamiliar predators. In this laboratory study, we tested the prediction that prior chemical exposure to a non-native predator feeding on conspecific tadpoles will subsequently allow tadpoles of the common toad (Bufo bufo) to recognize the chemical cues specifically released by this starved predator. Furthermore, we investigated the vulnerability of this chemically-mediated process to herbicide contamination. With these aims in view, groups of tadpoles were kept either unexposed or exposed for ten days to chemical cues from Turkish crayfish (Astacus leptodactylus) previously fed on tadpoles, both in uncontaminated water and in the presence of four sublethal concentrations of amitrole (0.01, 0.1, 1 and 10 mg.l⁻¹). We then assessed the effects of the six conditioning treatments on general activity and behavioural response to chemical cues from starved crayfish. Larval treatments did not affect the general activity of the tadpoles. By contrast, the treatments had significant effects on the behavioural response to the test solution prepared form starved crayfish. The only tadpoles to show an antipredator behavioural response to the chemical stimulation from starved crayfish belonged to the groups derived from chemical exposure to tadpole-fed crayfish in uncontaminated water and in contaminated water with the lowest concentration of amitrole (0.01 mg.l⁻¹). Conversely, this chemical stimulation produced no behavioural change in the control group or in the groups derived from exposure to tadpole-fed crayfish in contaminated water containing 0.1, 1 and 10 mg.l⁻¹ of amitrole. This study demonstrates that chemical cues released during the predator’s feeding activity can subsequently be used by common toad tadpoles in the recognition of an unfamiliar predator. In addition, our results show that the presence of sublethal amitrole concentrations can impair this recognition process. Such a pesticide effect might be especially detrimental for amphibian populations threatened by invasive predators.     

Fluorescence induction in the macroalgae Chondrus crispus (Rhodophyceae) and Ulva sp. (Chlorophyceae)

The induction of in vivo chlorophyll a (chl a) fluorescence (change in fluorescence intensity during a time-scale of ms to s) was measured to determine the potential of this technique for assessing the physiological condition of the macroalgae Chondrus crispus and Ulva sp. A gradient in variable fluorescence (P-F ₀ =peak minus initial fluorescence, a measure of Photosystem II activity) was found along the frond of C. crispus, the values increasing with distance from the thallus apex. No gradient was observed for Ulva sp. thalli. Nitrogen- or phosphorus-depleted Ulva sp. required a longer dark-conditioning period and had lower values of P-F ₀ than did controls. In contrast, no differences were found in P-F ₀ of N- or P-depleted C. crispus unless values were normalized to chl a. The irradiance history of C. crispus strongly influenced P-F ₀ , even after dark-conditioning: P-F ₀ declined by about 70% as the mean daily natural irradiance increased between 2 February and 14 March 1986; a negative correlation was observed between P-F ₀ and the photon flux density 1 d prior to the measurement; P-F ₀ remained elevated when C. crispus was grown under a low photon flux density; and P-F ₀ decreased in thalli within 5 d of transfer from growth under natural irradiance to an incubator with artificial irradiance. Changes in variable fluorescence at different growth irradiances of C. crispus may be due to adaptive changes in the relative absorption cross-section of this alga. The influence of irradiance history on Ulva sp. was minimal in comparison.Issued as NRCC No. 28730Part of this study was carried out while employed by Focal Marine Ltd., Bedford, Nova Scotia, Canada